Bangalore, Jan 19: A spacecraft launched by the European Space Agency (ESA) has sent back images of a 1500-km-long river valley on Mars. Reull Vallis is 300 metres deep and nearly seven kms wide at a particular point.
According to ESA, water used to flow across the Promethei Terra Highlands on the Red Planet. Before Reull Vallis ended up in the massive Hellas basin, at least one of its tributaries joined the main river.
The images captured by Mars Express show the valley's extremely sharp sides. The flow of ice and debris through the channel during the "Amazonian" period caused the longitudinal features which can be seen now on its floor. Back in the Hesperian period, water actually ran through the valley.
Since the adjacent craters contain lineated structures too, planetary scientists are of the opinion that Mars witnessed glacial activity in the distant past.
The discovery of Reull Vallis is very significant. It suggests that once Mars was almost habitable.
The US space agency NASA had earlier released pictures of another extra-terrestrial river system. High-resolution shots of a 400-km-long river on Titan, the huge moon of Saturn, were taken by the Cassini space probe.
However, there is no running water on Titan. It was ethane and methane that pooled into a large sea. Incidentally, the sea Kraken Mare covers 4 lakh sq kms.
Though the long river meanders, the fact that the river valley is more or less straight indicates the presence of fault lines. Jani Radebaugh who is associated with the Cassini radar team pointed out that "Such faults - fractures in Titan's bedrock -- may not imply plate tectonics, like on Earth, but still lead to the opening of basins and perhaps to the formation of the giant seas themselves."
The Titan river has been described as a "mini Nile". The longest river on Earth and lifeline of Egypt stretches 6700 kms.